3 i2 AUGUST WE ISM ANN [april 



would thus gradually have adapted itself to the changes in the body, 

 and to the new conditions resulting; from these changes as well as from 

 other causes ; it would have become localised and specialised. In 

 these animals no portion of the body can now give rise to a whole 

 animal, but the parts most exposed to injury, the appendages, have 

 retained the transmitted power of regeneration, and localised it in 

 certain parts, and in relation to definite stimuli. As in the course of 

 time the appendages of the different body-segments became more 

 widely differentiated in adaptation to different functions — giving 

 rise to antennae, jaws, walking-legs, or swimmerets — the predisposition 

 to regeneration in certain parts of the body slowly varied also ; and 

 thus, not indeed at the same rate, but not lagging very far behind, 

 the adaptation of the capacity for regeneration followed the adaptation 

 of a limb to a new function. 



Any one who has followed me in my attempt to formulate a theory 

 of regeneration will admit that all this thoroughly agrees with the 

 principles on which it is based, and will also see that it harmonises 

 with the theory of Natural Selection much better than any conception 

 of regeneration which has been or could be brought forward. It is 

 clear, for instance, that the variation of the regeneration -" Anlage " 

 must always take place much more slowly than that of the part itself — 

 in this case the appendage. For since Natural Selection consists in a 

 sifting out of the most fit, the rapidity with which it secures its 

 result — namely, transformation — -must depend, ceteris paribus, on the 

 number of individuals of a species which are selected in relation to 

 the part in process of transformation. If in a species of which one 

 million individuals are living at the same time, nine-tenths accidentally 

 perish, there will remain only 100,000 for the selection of the 1000 

 which we will assume to form the normal strength of the species. 

 The greater the number among these 100,000 possessing the favour- 

 able variation, the higher will be the number of the normally surviving 

 1000 possessing it, and the more rapid will be the progress of the 

 favourable variation. 



If, however, it be a question of the variation of a regeneration- 

 " Anlage," selection of its favourable variations will not operate 

 among the 100,000 individuals which chance has spared, but only 

 among those of them which, in the course of their life, lose the limb in 

 question and thus are in the position of having to renew it, well or 

 ill. Assuming that this is the case with ten per cent, selection 

 towards the improvement of the regeneration-apparatus would only 

 operate upon 1000 individuals, and the process of transformation of 

 the regeneration-" Anlage " would go forward much more slowly than 

 that of the transformation of the limb itself. 



Another fact must be noticed in the same connection. It has 

 already been observed in a series of cases, and would probably be 

 found to occur in many more if thorough investigation were made for 



